Pulmonary lymphatic system

The pulmonary lymphatic system contributes to the clearance of fluid and protein from the lung tissue interstitium and helps to prevent fluid accumulation in the lungs [108], The lymphatic endothelium allows micron-sized particles (e.g. lipoproteins, plasma proteins, bacteria and immune cells) to pass freely into the lymph fluid [103], After administration of aerosolised ultrafine particles into rats, particles were found in the alveolar walls and in pulmonary lymph nodes [135], which suggests that drainage into the lymph may contribute to the air-to-blood transport of the inhaled particles. 

From studies in spontaneous hypertensive rats, Aharinejad et al. (1999) suggested that pulmonary lymphatic filling is associated with pulmonary venous sphincters, and perivascular muscle action might be a component of the pulmonary lymphatic system. 

Dermal or intravenous exposure to lewisite leads to local skin edema and pulmonary edema due to increased capillary permeability. The increased capillary permeability results in blood plasma loss and resultant physiological responses collectively referred to as lewisite shock . Lewisite shock may be likened to shock observed in severe bum cases. It has been hypothesized that functional changes in the lungs, kidneys, respiratory tract, cardiovascular, and lymphatic systems may be the result of a disturbance of osmotic equilibrium (Goldman and Dacre, 1989). 

Intralymphatically injected oil contrast medium may remain in the lymph nodes for months or even for more than 1 year (150). The excess of that retained in the lymphatic system will enter the systemic veins through the thoracic duct or by way of lymphaticov-enous communications and eventually pass into the pulmonary artery and its branches, to be distributed in the lung capillaries. Experiments in the dog showed that 50% of the injected Ethiodol was found in the lung and about 23%inthe nodes at 3 days post-lymphography. The concentration of iodized oil in the nodes remained essentially the same but that in the lung had decreased to about 13% of the dose at 17 days postinjection (150,158). 

As in humans filariasis has high prevalence in domestic animals. The microfilariae live in the peritoneal blood and skin while the adult filariids reside in the blood vessels, lymphatic system, subcutaneous tissues and body cavities. In addition, the heartworm of the dog, Dirofilaria immitis, is found in the right ventricle and adjacent pulmonary arteries of carnivorous animals. 

No oral MRLs were derived for metallic (elemental) mercury due to the lack of data. Oral exposure to liquid metallic mercury would be expected to present little health risk, since it is so poorly absorbed (<0.01%) through the healthy intestine. Sufficiently large quantities could, however, present a risk of intestinal blockage, and some could enter the systemic circulation (blood or lymphatic) through open lesions, presenting a risk of occlusion of smaller arteries, especially within the pulmonary circulation. 

To maintain homeostasis, the continuous transudation of fluid and solutes from the pulmonary capillary bed into the surrounding inteistitium and alveolar space is balanced by lymphatic drainage out of the lung. The lymphatic flow is directed toward the hilum from the pleural surfaces. From lymph nodes in the hilum, the lymph travels to the paratracheal nodes and then eventually into the venous system via the thoracic duct. The lung has nerve fibers from both the vagal nerves parasympathetic) and the sympathetic nerves. The efferent fibers go to the bronchial musculature and the afferents come from the bronchi and alveoli. 

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